Nowadays many parts on an automobile seat are adjustable for reasons both of comfort and of health and safety. For example, the height of the headrest can be adjusted. The height and inclination of the lower part of the seat and its distance from the steering wheel can be adjusted. The inclination of the back can be adjusted, and it is possible to adjust supporting bodies which ensure a better lateral guidance of the upper part of the body. Supporting bodies supporting the spinal column, giving the pelvis a proper hold, and so on and so forth, can be adjusted. Numerous electric motors have hitherto been provided in the lower part of the seat and/or of the backrest. A separate electric motor has been assigned to most of the movement convertors. This immediately results in six to eight electric motors in an automobile seat. The individual electric motor has been selected, for example, by means of a rocker switch which has then actuated the movement convertor by a flexible shaft. The movement convertor is usually a worm drive, on the one had because a worm drive can easily be self-locking, and on the other hand because it allows a high reduction.
Disadvantages of the hitherto known technique are as follows:
a) The costs of DM 25.--for each electric motor are a tremendously high amount in series construction.
b) The electric motors considerably increase the weight. On the one hand, the seat becomes heavier. But on the other hand, the automobile also becomes heavier. This also has disadvantages in terms of fuel consumption, for example, because according to a rule of thumb a weight of 100 kg costs a liter of fuel over 100 km.
c) It is difficult to mount the electric motors in the seat, since a good fastening device must, of course, be provided for each electric motor.
d) Problems of space arise in a seat because of the volume of the electric motors, and they often have to be fastened where it is not advantageous per se.
e) With each electric motor, the error rate increases, for this is the lower, the fewer components are used.
f) In view of the above mentioned problems of space, the electric motors often have to be mounted where unfavorable noise conditions arise.
g) Again because of the volume of the electric motors, the backrest for example has to be made sufficiently thick to ensure that the electric motors have room. This means, for example, less leg room for the passengers sitting on the rear seat. This disadvantage necessarily has to affect the entire series, for in principle every seat must be provided with such adjusting devices. Even automobile models, in the seats of which no electric motor at all is installed, are therefore burdened by this disadvantage.
h) Every electric motor requires a feeder line and a discharge line. In view of the high currents, the cables have to be relatively thick, thus leading to the known disadvantages.
i) When there are defects, the upholstery of the seats often has to be opened and then closed again later.